Lazarides Theodore, Tart Nicholas M, Sykes Daniel, Faulkner Stephen, Barbieri Andrea, Ward Michael D
Department of Chemistry, University of Sheffield, Sheffield, UKS3 7HF.
Dalton Trans. 2009 May 28(20):3971-9. doi: 10.1039/b901560d. Epub 2009 Mar 10.
The complexes and contain M(bipy)(3) chromophores with a pendant aza-18-crown-6 macrocycle for binding of lanthanide(iii) ions. The photophysical properties of the adducts . and ., prepared by addition of excess Ln(NO(3))(3) (Ln = Nd, Yb) to solutions of and in MeCN, were examined using time-resolved and steady-state luminescence methods. Whereas does not act as an energy-donor to Yb(iii), it will transfer energy to (and generate sensitised near-infrared luminescence from) Nd(iii) with a Ru(ii)-->Nd(iii) energy-transfer rate constant of 6.8 x 10(6) s(-1). In contrast, is quenched by both Yb(iii) and Nd(iii), but with faster energy-transfer to Yb(iii) (2.6 x 10(7) s(-1)) than to Nd(iii) (1.4 x 10(7) s(-1)). Thus d --> f energy transfer is in both cases faster for Os(ii) than for Ru(ii), but the relative ability of Nd(iii) and Yb(iii) to act as energy-acceptors is inverted from . to .. Reasons for this are discussed with reference to contributions from the Förster and Dexter mechanism for energy-transfer in . and ., using calculated spectroscopic overlap integrals coupled with molecular modelling to estimate inter-chromophore separations. The particular effectiveness of Os(ii) --> Yb(iii) energy-transfer in . is explained in terms of the Horrocks redox mechanism involving an initial *Os(ii) --> Yb(iii) photoinduced electron transfer step generating an Os(iii)/Yb(ii) state, which is shown to be marginally favourable for ., but not for . in which the Ru(bipy)(3) unit is a poorer excited-state electron-donor by about 0.1 eV.
这些配合物含有M(bipy)(3)发色团，带有一个用于结合镧系(iii)离子的侧链氮杂-18-冠-6大环。通过向乙腈中的和的溶液中加入过量的Ln(NO(3))(3)（Ln = Nd，Yb）制备的加合物.和.的光物理性质，使用时间分辨和稳态发光方法进行了研究。虽然不能作为Yb(iii)的能量供体，但它会以6.8×10(6) s(-1)的Ru(ii)-->Nd(iii)能量转移速率常数将能量转移到Nd(iii)（并从Nd(iii)产生敏化近红外发光）。相比之下，被Yb(iii)和Nd(iii)都淬灭，但向Yb(iii)的能量转移速度（2.6×10(7) s(-1)）比向Nd(iii)的速度（1.4×10(7) s(-1)）更快。因此，在两种情况下，Os(ii)的d --> f能量转移都比Ru(ii)快，但Nd(iii)和Yb(iii)作为能量受体的相对能力从.到.发生了反转。参考.和.中能量转移的Förster和Dexter机制的贡献，结合计算的光谱重叠积分和分子建模来估计发色团间的距离，讨论了其原因。.中Os(ii) --> Yb(iii)能量转移的特殊有效性是根据Horrocks氧化还原机制来解释的，该机制涉及初始的*Os(ii) --> Yb(iii)光诱导电子转移步骤，产生Os(iii)/Yb(ii)状态，结果表明该状态对.略微有利，但对.不利，其中Ru(bipy)(3)单元作为激发态电子供体的能力约差0.1 eV。
